Abstract: Bridge Antiseismic System (BAS in abbreviation) is a software specifically designed for bridge seismic analysis, with functions of static analysis, response spectrum analysis and time history analysis. Spatial FEM model of bridge structures can be built with truss element, cable element, beam element, spring element and plate element. The overall features of BAS are firstly presented in this paper, and then the pre-process, analysis and post-process modules are discussed in details. Finally one practical bridge project is modeled in BAS, Midas and Sap2000 separately. The frequencies and the internal forces under self-weight, response spectrum and earthquake excitation are compared.